1. Field of the Invention:
This invention relates to a loudness control circuit for amplifying audio signals by emphasizing their low frequency components.
2. Description of the Related Art:
There are currently known a number of audio signal reproducing systems such as tape recorders, CD players and radio receivers. With these reproducing systems, amplification factors are sometimes adjusted for every frequency band, thereby changing the tone qualities to the listener's taste.
Portable reproducing systems are very popular. However, such portable reproducing system output sounds via a small headphone, and often suffer from insufficient low frequency tones because the system is very compact. In U.S. Pat. No. 4,982,435, the present inventor(s) has proposed a loudness control circuit which can emphasize low frequency components in such small portable reproducing system. With this system, only low frequency components are selected by low-pass filters, amplified, and reconstituted with audio signals from the entire frequency bands to emphasize the low frequency components.
Since it is usually operated by batteries and includes integrated circuits, the portable reproducing system cannot receive a large power supply voltage. Therefore, it is very difficult for a conventional loudness control circuit to amplify the low frequency components over a sufficient dynamic range.